Valve spring retainers are used in internal combustion engines to operatively retain a return spring on the stem of a poppet valve. Self-locking valve spring retainers are known in the art wherein the retainer automatically locks on the stem of the poppet valve as the retainer is pressed onto the valve stem. Self-locking valve spring retainers are advantageous in that they are easily installed in one quick motion by pressing onto the valve stem.
Examples of self-locking valve spring retainers are disclosed in U.S. Pat. Nos. 4,879,978 and 5,143,351, both to Pierce, the inventor of the subject invention. The subject matter of the aforementioned patents is included within the description of the subject invention by way of reference. Both of the Pierce references disclose self-locking valve spring retainers for operatively retaining a return spring on the stem of a poppet valve. Both of the references disclose an annular base ring and a plurality of arms extending in cantilever fashion from the base ring for flexing as the retainer is pressed over the end of the valve stem to an operative position. A self-locking means extends from each of the flexible arms for automatically engaging and gripping the valve stem when in the operative position.
Valve spring retainers are subjected to high shear stresses due to forces exerted thereon by very stiff return springs. Such shear stresses are focused about a small area of direct contact between the end of the valve stem and retainer. As a consequence of these shear stresses and the high temperature operating environment of an internal combustion engine, retainers may weaken and fail prematurely. U.S. Pat. No. 5,143,351 to Pierce addresses this problem by providing an independent metallic anti-wear plate disposed between the retainer and the end of the valve stem for distributing shear forces throughout the retainer instead of localized areas thereof. Although effective, the metallic anti-wear plate is somewhat difficult to install and further adds to the cost of the retainer.